Tuesday, August 6, 2013

UNIX is an open source operating system. It is a multiuser,
multitasking operating system and developed in 1969 at AT & T’s laboratory.
First, it was developed in assembly language but later it was recoded in ‘C’
language when this language developed by Dennis Ritchie. Actually, Unix is not
an operating system, it is trademark which we use to say, is it unix like
operating system or not. i.e. any operating follows the protocol which open
group created for unix, it can be called as Unix operating system. E.g. BSD,
HP-AX, Sequent, AIX.

Let’s talk about UNIX interview questions and its answers:

What is the difference between Linux and UNIX?

Ans -- If any operating system follows the UNIX protocols
then we can say that it is a unix operating system. E.g. BSD, HP-AX etc. In
case of Linux, actually Linux is a kernel which is most important part of
operating system. Operating system comprised kernel, device drivers, desktop,
other application etc. so, Linux is not an operating system, it is just a
kernel which operating system uses like Red hat Linux, Open Suse etc. These
operating system uses Linux kernel so, we can say that these operating systems
are Linux.

Which command can we use to rename the file in Unix?

Ans -- In unix, there is no separate command to rename the
file. We have to use ‘mv command’ to rename the file as below.

root@hello:~/hello/test#
ls

fil5 file1
file2 file3 file4 test1

root@hello:~/hello/test#

root@hello:~/hello/test#
mv file4 rename_file4

root@hello:~/hello/test#
ls

fil5 file1
file2 file3 rename_file4 test1

root@hello:~/hello/test#

Use of command:

mv source_file destination_file

What is sed?

Ans -- Sed is a stream editor used to parse and transform
the text. Sed does specified operations line by line on each line of input file
or stream. Sed script either command line script or separate file.

Is sed command edit file?

Ans -- Yes. Sed command can edit the file. But this feature
is available in Linux like operating only. This feature is not available in
Solaris.

What is alias and how to do it? What is the use of it?

Ans -- Alias used to map some letters to specific command
and instead of running that command, just type those letters. Please see below
example to map ‘ls –l’ command to ‘ll’ letters.

root@01hw394566:~/ctier/test#
alias

alias ls='ls
--color=auto'

root@01hw394566:~/ctier/test#

root@01hw394566:~/ctier/test#
alias ll='ls -l'

root@01hw394566:~/ctier/test#
alias

alias ll='ls -l'

alias
ls='ls --color=auto'

root@01hw394566:~/ctier/test#

root@01hw394566:~/ctier/test#
ll

total 4

-rw-r--r-- 1
root root 0 2013-07-30 20:09 fil5

-rw-r--r-- 1
root root 0 2013-07-30 20:09 file1

-rw-r--r-- 1
root root 0 2013-07-30 20:09 file2

-rw-r--r-- 1
root root 0 2013-07-30 20:09 file3

-rw-r--r-- 1
root root 0 2013-07-30 20:09
rename_file4

-rw-r--r-- 1
root root 20 2013-07-30 20:09 test1

root@01hw394566:~/ctier/test#

Which daemons are running for NFS service?

Ans -- There are many NFS service daemons are running when
we start the service. These daemons as follows:

Nfs

Nfsblock

Rpcbind

Rpc.mountd

Rpc.nfsd

Lockd

Rpc.statd

Rpc.rquotad

Rpc.idmapd

What is NFS port number and main configuration file?

Ans -- NFS service is using 2049 port and its main
configuration file is /etc/exports.

If you have seen in above example, we see that after
stripping html tags, there are blank lines as it is. That’s why, we have used
sed again to strip all blank lines.

What is inode?

Inode is a data structure found in unix file system. Each
inode stores all the information about a file system object except data content
and file name. We can see any file’s inode by command as “ls –i file name”.
Inode is a unique in a file system. Inode contains following information:

File Type

Permissions (read, write, execute)

Owner

Group

File Size

File access, change, modification time

File deletion time

Number of links

Access control list

How do I see a inode number of file?

Ans – Please see below example.

root@01hw394566:~/ctier/test#
ls –li

total 8

1206521 -rw-r--r-- 1 root root 0 2013-07-30 20:09 fil5

1206512 -rw-r--r-- 1 root root 0 2013-07-30 20:09 file1

1206515 -rw-r--r-- 1 root root 0 2013-07-30 20:09 file2

1206516 -rw-r--r-- 1 root root 0 2013-07-30 20:09 file3

1206559 drwxr-xr-x 2 root root 4096
2013-08-05 21:39 how

1206517 -rw-r--r-- 1 root root 0 2013-07-30 20:09 rename_file4

1206556 -rw-r--r-- 1 root root 20
2013-07-30 20:09 test1

1206560 -rw-r--r-- 1 root root 72
2013-08-05 20:22 test.html

root@01hw394566:~/ctier/test#

How to check port is open or not in Unix?

Ans— We can check port is open or not in Unix by netstat
command. Please see below example for checking for port 80.

root@01hw394566:~/ctier/test#
netstat
-aeen | grep -w 80

tcp 0
0 127.0.0.1:80 0.0.0.0:* LISTEN 0 8817

root@01hw394566:~/ctier/test#

If you see port 80 is tcp port. We have used double e option
to get more detailed information about this port.

If you want to read more interview questions for Linux
Administrator then click on below Link.